The invention relates to the controlled inflation of balloon cuffs which surround the end of tracheal tubes used in respiratory medicine. Tracheal tubes include both tracheostomy and endotracheal tubes. An endotracheal tube is one which can quickly be inserted through the mouth or nose into the trachea, while a tracheostomy tube must be inserted through a surgical opening in the neck. However for the purposes of this invention, they may be viewed as the same, and will therefore herein be referred to collectively as tracheal tubes, unless otherwise stated.
Tracheal tubes may be inserted for a variety of reasons, including, the need for mechanical ventilation, bypass of an obstruction, removal of secretions, easier ventilation due to less dead space. In most circumstances, it is necessary to seal the outside of the tracheal tube to the inner tracheal lining, i.e., the tracheal mucosa. During mechanical ventilation, this is particularly true, since a closed circuit is necessary for a ventilator to force a given volume of air or oxygen under pressure into a patient's lungs. When a patient is not being mechanically ventilated, a seal may or may not be required. In this situation, the need for a seal will generally depend on whether or not there is a risk of aspiration. In the case of an endotracheal tube, this risk is always present, while with a tracheostomy tube, this risk is often present. Therefore, most patients require a seal either to prevent aspiration or to create a closed circuit for mechanical ventilation. Because of the pressurization of the system, a tighter seal is necessary during mechanical ventilation than is necessary to prevent aspiration in the absence of mechanical ventilation.
It is well known that over-pressurization of the tracheal cuff can cause significant tracheal damage including hemorrhage, ulcers, perforation, and strictures. It is generally accepted that the main cause of this damage is occlusion of blood vessels leading to loss of blood flow with resultant necrosis of the tracheal lining. Experience has shown that an intra cuff pressure of less than 25 cm H.sub.2 O is associated with significantly fewer complications. This is consistent with experimental data suggesting that the capillary perfusion pressure in the tracheal mucosa is in the range of 30-40 cm H.sub.2 O. Thus, a cuff pressure of 25 cm H.sub.2 O would still allow some blood flow. However, the numbers noted above are not absolute. Damage is occasionally seen with cuff pressures of 25 cm H.sub.2 O because perfusion pressures may be lower than expected due, for example, to low blood pressure. Therefore, the best approach is to use the lowest cuff pressure consistent with an adequate ventilation seal and the prevention of aspiration.
Tracheal cuffs are frequently positional, that is, as the patient moves, the balloon moves into tighter and looser positions within the trachea. This causes the pressure in the cuff to increase and decrease respectively. The result is either too much pressure on the mucosa or a pressure leak. The problem of tracheal tube movement is not just a theoretical one. The phrases "positional tube" or "positional cuff" are ones frequently heard in practice to report a condition in which, after proper inflation of a cuff, movement of the patient causes excessive, often audible leakage of the ventilator volume around the cuff. In this case, the patient's lungs fail to receive the prescribed volume. In addition, the loss of a seal between the cuff and trachea allows aspiration to occur.
A further cause of loss of a seal with resultant aspiration and leakage of ventilator volume is a leak in the cuff itself or in the cuff inflation line.
Problems relating to tracheal cuff pressure control and monitoring have been the subject of numerous articles in the medical literature over the years. To summarize, the problem is to achieve cuff pressures high enough to prevent aspiration and loss of ventilator volume without causing any damage to the tracheal mucosa. Solving this problem has been particularly difficult because of the wide range of clinical conditions in which the cuff system is required to function. For example, in the setting of an irregular trachea, stiff lungs requiring high pressures to ventilate, and low blood pressure, the minimum cuff pressure needed to prevent loss of ventilator volume might cause mucosal damage.
Over the years numerous tracheal tubes and cuff pressure controllers have been designed and patented for the purpose of improved cuff pressure control. To date no completely satisfactory system has been designed which solves the problems of tracheal cuff control and monitoring.
The tracheal tubes have one thing in common, namely, they all have one inflation line communicating with the cuff for the purpose of inflating it. Several tracheal tubes have been designed with two cuffs. However, each cuff has a single inflation line. There are two major problems with the existing tracheal tubes. In the first place, existing inflation lines are of a small diameter ranging from 0.015"-0.030". While this diameter is satisfactory for slowly inflating a cuff, it is inadequate for rapid, synchronous inflation and deflation of a tracheal cuff. Because of the small diameter, the high resistance to flow does not allow rapid enough inflation and deflation of the tracheal cuff at the low pressures which are used for tracheal cuff inflation. The second problem is that it is not possible to synchronously inflate and deflate a cuff, and continuously monitor cuff pressure through a single inflation lumen. This is because the resistance of the inflation lumen causes significant pressure differential between the external applied pressure and the actual intracuff pressure. The greater the flow through the inflation lumen, the greater the difference between applied pressure and actual pressure in the cuff.
In addition to numerous tracheal tube designs, a number of tracheal cuff controllers have been designed, for the purpose of more accurately applying pressure to the tracheal tube cuff. These systems have generally over-pressurized cuffs for different reasons. In most cases they have not allowed continuous bidirectional cuff pressure control. In other cases, the application of PEEP was communicated to the cuff pressure, while in other cases too much baseline pressure was applied to the cuff.
In my previous patent (U.S. Pat. No. 4,924,862) I describe a "Pressure Controller and Leak Detector for Tracheal Tube Cuff". That design solved many of the problems of tracheal cuff control. I herein describe a new tracheal tube to be used in association with a significantly improved Pressure Controller and Leak Detector.